The field of the invention relates to force transducers fabricated from silicon.
It is known to fabricate force transducers of the parallel plate capacitive type by etching a flexible plate or diaghragm from a silicon substrate and bonding the substrate to a second parallel substrate with an insulating spacer therebetween. Conventional electronic circuitry is employed to measure the change in capacitance resulting from flexure or bending of the diaphragm thereby providing an approximation of the force applied against the diaphragm. An example of this type of transducer is disclosed in U.S. Pat. No. 4,495,820. A problem with this type of approach is that the diaphragm must be sufficiently thick to avoid either fracture or contact between the plates thereby limiting the sensitivity of the device. Stated another way, since sensitivity is inversely related to diaphragm thickness, and the diaphragm must be sufficiently thick to avoid both fracture and plate contact, there is a limit on the device sensitivity. Another problem is that because the diaphragm flexes or bends, deflection of the diaphragm is not rectilinear in response to the applied force. Thus, the required translation of diaghragm deflection into a measurement of the applied force is complicated. Still another problem is the fabricating complexity of bonding together two separate structures.
U.S. Pat. No. 4,144,516 issued to Aine discloses adjacent folded cantilever leaf springs etched from a silicon substrate wherein leaf spring deflection is, allegedly, linearly proportional to the applied force. The disclosed device however still requires multiple substrates to be bonded together and it also appears to have limited sensitivity.
U.S. Pat. No. 4,665,610 issued to Barth discloses a pressure transducer having multiple level diaphragms formed by etching a selectively etchable material, or spacer, between the diaphragm levels. This approach does not appear to provide rectilinear displacement of the diaghragm in response to the applied force. Another disadvantage is the inherent complexity in fabricating the multiple level diaphragms.